Brain wiring needed for reading isn’t learned—it’s in place prior to reading

Researchers could predict how kids’ brains would develop before they learned to read.

Our brains are apparently really good at divvying up heavy mental loads. In the decades since scientists started taking snapshots of our noggins in action, they’ve spotted dozens of distinct brain regions in charge of specific tasks, such as reading and speech. Yet despite documenting this delegation, scientists still aren’t sure exactly how slices of our noodle get earmarked for specific functions. Are they preordained based entirely on anatomy, or are they assigned as wiring gets laid down during our development?

A new study, published this week in Nature Neuroscience, adds more support for that latter hypothesis. Specifically, researchers at MIT scanned the brains of kids before and after they learned to read and found that they could pinpoint how the area responsible for that task would develop based on connectivity patterns. In other words, the neural circuitry and hookups laid down prior to reading determined where and how the brain region responsible for reading, the visual word form area, or VWFA, formed.

“Long-range connections that allow this region to talk to other areas of the brain seem to drive function,” Zeynep Saygin, lead study author and researcher at MIT’s McGovern Institute for Brain Research, said in a news release.

The finding squares with researchers’ hunch that connectivity is key, plus previous findings from studies done on ferrets. In those experiments, researcher manually re-wired the brains of the developing mustelids, rerouting the input wires from the retina to a region of the brain normally tasked with handling sound input. In response, that auditory cortex developed distinct functions involved with vision. Thus, it's connectivity, not other intrinsic features of brain regions, that might explain functional divisions, the researchers speculated.

Taking the hypothesis from the basic sensory functions of cute furry critters to the higher mental tasks of humans, the MIT researchers picked on reading and the development of the VWFA. Reading among humans is a unique mental feat, having only developed some 5,400 years ago. That’s not long enough for our brains to have evolved a special region dedicated to reading. Yet, the VWFA, which sits at the base of the brain in the fusiform gyrus (see diagram), distinctly and specifically responds to visually presented words or letter strings and not other visual stimuli, such as numbers or faces.

Saygin and colleagues scanned the brains of 14 kids at age five, before they could read, and again at age eight, after they had learned and formed their VWFA. They used both functional magnetic resonance imaging (fMRI), which indicates brain activity based on blood flow, and diffusion-weighted MRI (DWI), which can help trace connections in the brain.

Prior to learning to read, the area that would later become the VWFA didn’t respond differently when the kids looked at words versus other objects, the researchers found. But based on the DWI data, that area had distinct connection patterns from the surrounding brain regions. Those patterns were enough for the researchers to precisely predict how the VWFA would form by the time the kids were eight.

“These findings powerfully support the idea that earlier-developing patterns of connectivity instruct the development of cortical regions into functionally distinct regions,” the authors conclude. Now, how “distinctive connectivity arises before distinctive function” is a question for more research.

Saygin speculates that in humans’ past, the area that now becomes the VWFA may have been involved in higher-level perception of objects before being coopted to reading. But knowing that the takeover will happen when kids learn to read may give researchers a way to look ahead. By peeking at brain connections prior to the VWFA forming, doctors may be able to anticipate years in advance if kids will have reading difficulties or disorders such as dyslexia.

“This could be a way to use neuroimaging to try to actually help individuals even before any problems occur,” Saygin said.